The plant TPX2 protein regulates prospindle assembly before nuclear envelope breakdown.
The Targeting Protein for Xklp2 (TPX2) is a central regulator of spindle assembly in vertebrate cells. The absence or excess of TPX2 inhibits spindle formation. We have defined a TPX2 signature motif that is present once in vertebrate sequences but twice in plants. Plant TPX2 is predominantly nuclear during interphase and is actively exported before nuclear envelope breakdown to initiate prospindle assembly. It localizes to the spindle microtubules but not to the interdigitating polar microtubules during anaphase or to the phragmoplast as it is rapidly degraded during telophase. We characterized the Arabidopsis thaliana TPX2-targeting domains and show that the protein is able to rescue microtubule assembly in TPX2-depleted Xenopus laevis egg extracts. Injection of antibodies to TPX2 into living plant cells inhibits the onset of mitosis. These results demonstrate that plant TPX2 already functions before nuclear envelope breakdown. Thus, plants have adapted nuclear-cytoplasmic shuttling of TPX2 to maintain proper spindle assembly without centrosomes.
Vos
Jan W
JW
Laboratory of Plant Cell Biology, Wageningen University, 6703 BD Wageningen, The Netherlands.
Pieuchot
Laurent
L
Evrard
Jean-Luc
JL
Janski
Natacha
N
Bergdoll
Marc
M
de Ronde
Dryas
D
Perez
Laurent H
LH
Sardon
Teresa
T
Vernos
Isabelle
I
Schmit
Anne-Catherine
AC
D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D002467:Cell Nucleus / Q000378:metabolism / Q000648:ultrastructure; D002473:Cell Wall / Q000378:metabolism*; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D008869:Microtubule-Associated Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D008870:Microtubules / Q000378:metabolism / Q000648:ultrastructure; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009685:Nuclear Envelope / Q000378:metabolism*; D021382:Protein Sorting Signals; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000187:drug effects; D016415:Sequence Alignment; D020539:Sequence Analysis, Protein; D008941:Spindle Apparatus / Q000378:metabolism*; D014026:Nicotiana / Q000166:cytology / Q000187:drug effects / Q000235:genetics; D014981:Xenopus; D028901:alpha Karyopherins / Q000378:metabolism
D000906:Antibodies; D029681:Arabidopsis Proteins; D005231:Fatty Acids, Unsaturated; D008869:Microtubule-Associated Proteins; D021382:Protein Sorting Signals; C535123:TPX2 protein, Arabidopsis; D028901:alpha Karyopherins; C038753:leptomycin B